Thursday, December 4, 2008

Determination of pressure coefficient : Jolly’s bulb method.

Description:

Consider a bulb (A) kept in a container and is attached to a doubly bent glass tube. The other end of the tube is connected to a rubber tube, and the rubber tube is connected to a reservoir. The reservoir is attached to a retard stand and it is free to move on the retard stand. A vertical scale is fixed behind the rubber tube to measure the pressure.

Procedure:

Send dry air into the glass bulb several times and moisture should be removed from the glass bulb. Now the glass bulb is filled with dry air and the reservoir is partially filled with mercury. Ice cubes are kept in the container, so that the glass bulb attains 00c temperature and the gas is cooled. Now mark the mercury level on the rubber tube. The level difference in the two limbs can be measured by the vertical scale and is noted as h1. The atmospheric pressure H can be measured by Fortin’s Barometer.

The pressure at this temperature is noted as P0 = H ±h1.

Now the ice cubes are replaced with water and the water is boiled upto temperature T. Temperature can be measured by thermometer . After some time the bulb atains the temperature as the water and the volume of the gas increases. The mercury in the rubber tube moves down. But we have to find the pressure at this temperature at constant volume, for that we have to raise the reservoir till the mercury in the left limb reached point M. Now fix the reservoir and the level difference in the two limbs is measured by the vertical scale.

The pressure at this temperature is noted as Pt = H ±h2.

Pressure co-efficient of the gas can be measured by β = (Pt-P0)/(P0 t).

Result of the Experiment

Experimental result gives the Pressure coefficient of air as 0.003671/0C . or 1/ 273.16/0C.

Precautions:

Volume of the air must be constant throughout the experiment .Before the experiment the apparatus must be cleaned with dry air properly.

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